This invention relates to single-wall carbon nanotube/polymer composites, a process for the production of such, and their use as fibers, films and articles.
Carbon nanotubes were first reported in 1991 by Sumio Iijima who produced multilayer tubules by evaporating carbon in an arc discharge. These linear fullerenes are attracting increasing interest as constituents of novel nanoscale materials and device structures. Defect-free nanotubes are expected to have remarkable mechanical, electronic and magnetic properties that will be tunable by varying the diameter, number of concentric shells, and chirality of the tube.
In 1993, Iijima""s group and an IBM team headed by D. S. Bethune independently discovered that a single-wall nanotube could be made by vaporizing carbon together with a transition metal such as iron or cobalt in an arc generator (see Iijima, et al., Nature, Vol. 363, p. 603, (1993); D. S. Bethune et al., Nature 363 (1993) 605 and U.S. Pat. No. 5,424,054). These syntheses produced low yields of non-uniform nanotubes mixed with large amounts of soot and metal particles.
Richard Smalley et al. in Chem. Phys. Letters, Vol. 243 (1995) 49-54 disclose a process for making single-wall nanotubes having diameters of about 1 nm and lengths of several microns. The nanotubes aggregated into xe2x80x9cropesxe2x80x9d in which many tubes were held together by van der Waals forces. The nanotubes produced were remarkably uniform in diameter.
In later work published in Science, Vol. 273 (1996) 483-487, Smalley et al. discuss the addition of a second laser to their process which gives a pulse 50 nanoseconds after the pulse of the first laser. This raised the yield of nanotubes to an estimated range of 70 to 90% and seemingly favored the 10, 10 configuration (a chain of 10 hexagons around the circumference of the nanotube). The product consisted of fibers approximately 10 to 20 nm in diameter and many micrometers long comprising randomly oriented single-wall nanotubes, each nanotube having a diameter of about 1.38 nm.
J. Liu et al. in xe2x80x9cFullerene Pipesxe2x80x9d, Science, Vol. 280 (1998) 1253 discusses single-wall fullerene nanotubes that are converted from nearly endless, highly tangled ropes into short, open-ended pipes that behave as individual macromolecules. Also described therein is the termination of the open ends of the nanotubes with carboxylic acid groups after treatment in acid. This is followed by reaction with SOCl2 at room temperature to form the corresponding acid chloride.
Because of their unique electronic and mechanical properties, further progress toward new uses of single-wall nanotubes is desirable.
The present invention relates to a single wall carbon nanotube/polymer composite, comprising a single wall carbon nanotube having at least one end chemically bonded to a polymer.
The present invention also relates to a process for producing a single wall carbon nanotube/polymer composite, comprising the steps of:
(a) contacting single wall carbon nanotubes with an acid, wherein at least a portion of said carbon nanotubes form acid derivatized nanotubes, each of said acid derivatized nanotubes having at least one carboxylic acid attached to at least one end of the nanotube;
(b) contacting the product of step (a) with one or more polymer precursors to form a pre-polymer product; and
(c) polymerizing the pre-polymer product of step (b) to form a single wall carbon nanotube/polymer composite.
The present invention further provides a fiber comprising the single wall carbon nanotube/polymer composite described above.
The present invention also provides an article comprising the single wall carbon nanotube/polymer composite described above.
The present invention also provides a film comprising the single wall carbon nanotube/polymer composite described above.
In accordance with a first embodiment of the present invention, there is provided a single wall carbon nanotube/polymer composite. The present composite comprises a nanotube component and a polymer component. The nanotube component comprises single wall carbon nanotubes each individually having a length ranging from about 10 to about 300 nm and each nanotube having a diameter ranging from about 1 to about 2 nm. At least one end of a portion of the nanotubes present within the composite is derivatized and chemically bonded to or within one or more chains of a polymer of the polymer component via one or more chemical bonds. Thus, there can be a derivatized nanotube bearing a carboxyl group at one end that can serve as a chain-terminating group of a polymer chain of the polymer component. A nanotube bearing carboxyl groups at both ends is capable of copolymerization and can reside at the end of or within the polymer chain. Thus, the derivatized nanotubes can reside at the end of polymer chains, within the polymer chains, or both. The composites of the present invention can be described as block copolymers in which the nanotubes are the hard segment.
As used herein a single wall carbon nanotube refers to a hollow carbon fiber having a wall consisting essentially of a single layer of carbon atoms. Single wall carbon nanotubes can be made by the processes disclosed in lijima et al., Nature, Vol. 363, p. 603 (1993); D. S. Bethune et al., Nature 63 (1993) 060, U.S. Pat. No. 5,424,054, R. Smalley et al, Chem. Phys. Letters, Vol. 243 (1995) 49-54 and Science Vol. 273 (1996) 483-487.
The polymer component of the present composite comprises polymers, including copolymers, capable of chemically bonding to a derivatized end of a single wall carbon nanotube or those polymers that can be prepared from one or more monomer precursors capable of bonding with a derivatized end of a single wall carbon nanotube either prior to or during polymerization. Representative examples of polymers comprising the polymer component of the present invention include linear and branched polyamides, polyesters, polyimides and polyurethanes. Preferred polyamides include but are not limited to nylon 6; nylon 6,6; and nylon 6,12. Preferred polyesters include but are not limited to poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(trimethylene naphthalate).
In accordance with the present invention, there is provided a process for preparing a single wall carbon nanotube/polymer composite. The process comprises the steps of preparing an acid derivatized nanotube, contacting the derivatized nanotube with one or more polymer precursors to form a pre-polymer product and polymerizing the pre-polymer product to form the single wall carbon nanotube/polymer composite.
Prior to forming the acid derivatized nanotube, it may be necessary to cut the nanotubes and optionally purify them. Highly tangled ropes of nanotubes currently available or produced by the methods referenced above can be cut into short lengths of open tubes of about 10 to 300 nm in length. The cut tubes can then be suspended, sorted, and manipulated as individual macromolecules (see Liu et al., Science, Vol. 280, 1253-1256, 1998).
Since the nanotubes produced by the methods currently available may contain impurities, such as bucky onions, spheroidal fullerenes, amorphous carbon, and other material, that are difficult to separate from the nanotubes once they have been cut, it is preferable to purify the nanotube material before cutting. A suitable purification method comprises refluxing in 2.6 M nitric acid and resuspending the nanotubes in pH 10 water with surfactant, such as sodium lauryl sulfate, followed by filtration with a cross-flow filtration system. The resultant purified single wall nanotube suspension can be passed through a polytetrafluoroethylene filter to produce a freestanding mat of tangled single wall nanotube ropes. Preferably, the ropes are not allowed to dry since that can make redispersion more difficult.
Alternatively, purified single wall nanotubes in aqueous suspension can be purchased from Tubes@Rice, MS-100, P.O. Box 1892, Houston Tex. 77251-1892 or Carbolex Inc., ASTeCC Building, University of Kentucky, Lexington, Ky. 40506-0286.
The nearly endless ropes of nanotubes can then be cut to make ends by several techniques ranging from simply cutting with a pair of scissors to bombardment with relativistic gold ions. However, a far more effective and efficient method for cutting is prolonged sonication of the nitric acid-purified single wall nanotube rope material in an oxidizing acid, such as a mixture of concentrated sulfuric and nitric acids, at 40xc2x0 C.
Before chemically cutting the nanotubes, it is best to remove the surfactant. This can be accomplished by diluting a quantity of the surfactant/water mix with an equal volume of methanol. This mixture can then be centrifuged at about 20,000 g for at least 20 minutes and decanted. This procedure can be repeated adding just as much methanol as was done the first time. Then, the procedure can be repeated again, except that dimethyl formamide (DMF) can be added instead of methanol. Finally, the mixture can be diluted to the desired concentration with DMF. If the solution is thoroughly homogenized after each dilution, this procedure can suspend the nanotubes in DMF. Alternatively, instead of the final suspension in DMF, the nanotubes can be filtered and transferred immediately to the oxidizing acid to commence chemical cutting.
After the nanotubes are cut and after further optional treatment in acid, at least a portion of the open ends of the nanotubes are presumed to be terminated with one or more carboxylic acid groups (see K. Kinoshita, Carbon Electrochemical and Physico-chemical Properties, Wiley, N.Y., 1988, pp. 199-201).
Such acid derivatized carbon nanotubes can be added to and subsequently copolymerized with precursors of polymers including but not limited to monomeric precursors to polyamides, polyesters, polyimides, or polyurethanes. For example, the acid derivatized carbon nanotubes can be contacted with a diacid and a diamine and the resultant pre-polymer product polymerized to form a single wall carbon nanotube/polyamide composite, or the acid derivatized carbon nanotubes can be contacted with a diacid or a diester, and a diol and the resultant pre-polymer product polymerized to form a single wall carbon nanotube/polyester composite.
The diacid can be selected from aliphatic, alicyclic or aromatic diacids. Specific examples of such acids include glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid; 1,2- or 1,3-cyclohexane dicarboxylic acid; 1,2-or 1,3-phylene diacetic acid; 1,2- or 1,3-cylohexane diacetic acid; isophthalic acid; terephthalic acid; 4,4xe2x80x2-oxybis(benzoic acid); 4,4xe2x80x2-benzophenone dicarboxylic acid; 2,5-naphthalene dicarboxylic acid; and p-t-butyl isophthalic acid. The preferred dicarboxylic acid for a polyamide component is adipic acid.
The diamine can be aliphatic, alicyclic or aromatic diamines. Specific examples of such diamines include hexamethylene diamine; 2-methyl pentamethylenediamine; 2-methyl hexamethylene diamine; 3-methyl hexamethylene diamine; 2,5-dimethyl hexamethylene diamine; 2,2-dimethylpentamethylene diamine; 5-methylnonane diamine; dodecamethylene diamine; 2,2,4- and 2,4,4-trimethyl hexamethylene diamine; 2,2,7,7-tetramethyl octamethylene diamine; meta-xylylene diamine; paraxylylene diamine; diaminodicyclohexyl methane and C2-C16 aliphatic diamines which can be substituted with one or more alkyl groups A preferred diamine is hexamethylene diamine.
Alternative precursors for preparing a polyamide component of a single wall carbon nanotube/polyamide composite include compounds having a carboxylic acid functional group and an amino functional group or a functional precursor to such a compound which compounds include 6-aminohexanoic acid, caprolactam, 5-aminopentanoic acid, 7-aminoheptanoic acid, and the like.
The diacid or diester polymer precursors useful in preparing a polyester component of the present composite, suitably include aliphatic dicarboxylic acids which contain from 4 to 36 carbon atoms, diesters of aliphatic dicarboxylic acids which contain from 6 to 38 carbon atoms, aryl dicarboxylic acids which contain from 8 to 20 carbon atoms, diesters of aryl dicarboxylic acids which contain from 10 to 22 carbon atoms, alkyl substituted aryl dicarboxylic acids which contain from 9 to 22 carbon atoms, or diesters of alkyl substituted aryl dicarboxylic acids which contain from 11 to 22 carbon atoms. The preferred aliphatic dicarboxylic acids contain from 4 to 12 carbon atoms. Some representative examples of such aliphatic dicarboxylic acids include glutaric acid, adipic acid, pimelic acid and the like. The preferred diesters of alkyl dicarboxylic acids contain from 6 to 12 carbon atoms. The preferred aryl dicarboxylic acids contain from 8 to 16 carbon atoms. Some representative examples of aryl dicarboxylic acids are terephthalic acid, isophthalic acid and orthophthalic acid. The preferred diesters of aryl dicarboxylic acids contain from 10 to 18 carbon atoms. Some representative examples of diesters of aryl dicarboxylic acids include dimethyl terephthalate, dimethyl isophthalate, dimethyl orthophthalate, dimethyl naphthalate, diethyl naphthalate and the like. The preferred alkyl substituted aryl dicarboxylic acids contain from 9 to 16 carbon atoms and the preferred diesters of alkyl substituted aryl dicarboxylic acids contain from 11 to 15 carbon atoms.
Diols useful as polymer precursors in the present invention herein suitably comprise glycols containing from 2 to 12 carbon atoms, glycol ethers containing form 4 to 12 carbon atoms and polyether glycols having the structural formula HOxe2x80x94(AO)nH, wherein A is an alkylene group containing from 2 to 6 carbon atoms and wherein n is an integer from 2 to 400. Generally, such polyether glycols will have a molecular weight of about 400 to 4000.
Preferred glycols suitably contain from 2 to 8 carbon atoms, with preferred glycol ethers containing from 4 to 8 carbon atoms. Some representative examples of glycols, which can be employed as a diol polymer precursor, include ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 2,2-diethyl-1,3-propane diol, 2,2-dimethyl-1,3-propane diol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propane diol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, 2,2,4-trimethyl-1,6-hexane diol, 1,3-cyclohexane dimethanol, 1,4-cyclohexane dimethanol, 2,2,4,4,-tetramethyl-1,3-cyclobutane diol, and the like A representative example of polyether glycol is Polymeg(copyright) and of polyethylene glycol is Carbowax(copyright).
Preferred polyesters for the polymer component of the present composite include for example, poly(ethylene terephthalate)(PET), poly(ethylene naphthalate)(PEN), poly(trimethylene terephthalate)(3G-T), and poly(trimethylene naphthalate)(3G-N).
Following contact of the acid derivatized carbon nanotubes with the polymer precursors, the pre-polymer product of such contact may be filtered, washed, and dried. For example, this procedure would be appropriate for treatment of the salt precipitate when using polyamide precursors. In addition, for the formation of other pre-polymer products, water or alcohol may be removed such as in the formation of polyester pre-polymers.
The pre-polymer product resulting from the contact of the acid derivatized carbon nanotubes and the polymer precursors can be polymerized under the pressure, temperature and other process conditions suitable for the polymerization of the particular polymer precursors present. This may include the addition of a catalyst. The resultant product comprises a single wall carbon nanotube/polymer composite.
Alternatively, in the process of the present invention, following the step in which the nanotube is acid derivatized, any carboxylic acid groups of the nanotube ends described above can be converted to the corresponding acid chlorides by reactions known by those of skill in the art, such as by contact with SOCl2 at room temperature.
The acid chloride derivatized carbon nanotube can then be contacted with an excess of a diamine. Upon contact with the diamine, such as those listed above, an amine derivatized carbon nanotube can be formed whereby an amide linkage is formed to the nanotube and the free amine on the other end of the nanotube is available for further reaction.
For example, such amine derivatized carbon nanotubes can be contacted with a diacid and a diamine, which can be the same or different from the diamine used to prepare the amine derivatized nanotube, to form a pre-polymer product comprising a polyamide salt. Upon polymerization of the pre-polymer product resulting from the contact of the acid derivatized nanotube with the acid chloride followed by contact with diamine, a single wall carbon nanotube/polyamide composite will result.
Alternatively, the amine derivatized carbon nanotube can be contacted with a pyromellitic dianhydride to form a nanotube/polyimide composite upon polymerization. Similarly, a single wall carbon nanotube/polyurethane composite can be formed by contacting an amine derivatized nanotube with an isocyanate, such as toluene diisocyanate, followed by polymerization.
Further, in accordance with the present invention, there is provided a fiber comprising the nanotube/polymer composite described above. After formation of the nanotube/polymer composite, a fiber can be formed therefrom by cutting the composite material into chips and drying. These chips can then be heated under pressure to bond the chips into a plug. This plug can then be heated to a molten state, passed through a mesh screen, and forced through an extrusion orifice. The filament formed by the molten composite material can then be pulled away from the orifice and wound onto a bobbin. Such fibers can be incorporated into bulked continuous filament yams and made into carpets. Such carpets have inherent antistatic properties.
Further, in accordance with the present invention, there is provided an article comprising the nanotube/polymer composite described above. After formation of the nanotube/polymer composite, the composite material can be used as an injection moldable resin for engineering polymers for use in applications including solenoid bodies for automotive braking systems.
Further, in accordance with the present invention, there is provided a film comprising the nanotube/polymer composite described above. Preferably, the polymer component of the composite is a polyester. After formation of the nanotube/polymer composite, the composite material can be melt extruded to form a film. Such films are useful in applications including static-free packaging for electronic components.